Stacked piezoelectric diaphragm members

ABSTRACT

A diaphragm assembly ( 20 ) comprises at least two piezoelectric diaphragm members ( 22 ) arranged in a stacking direction ( 23 ). An interface layer ( 24 ) is situated between adjacent piezoelectric diaphragm members ( 22 ). The interface layer ( 24 ) in the stacking direction ( 23 ) is displaceable but incompressible. The interface layer ( 24 ) permits lateral movement of the adjacent piezoelectric diaphragm members ( 22 ) relative to the interface layer ( 24 ) in a direction perpendicular to the stacking direction ( 23 ). The interface layer ( 24 ) can comprise, for example, an incompressible liquid or a semi-liquid. A gasket ( 26 ) can be used to seal the incompressible substance in the interface layer if necessary.

BACKGROUND

1. Field of the Invention

The present invention pertains to piezoelectric diaphragms, andparticularly to a piezoelectric diaphragm assembly with stackeddiaphragms and/or a pump incorporating the same.

2. Related Art and Other Considerations

A piezoelectric material is permanently-polarized and will produce anelectric field when the material changes dimensions as a result of animposed mechanical force. This phenomenon is known as the piezoelectriceffect.

Layers of piezoelectric material can be stacked to form a multiple layerpiezoelectric device. For example, U.S. Pat. No. 6,215,228 to Yamazakidiscloses stacking multiple piezoelectric layers and multiple internalelectrodes. U.S. Pat. No. 5,245,734 to Issartel discloses stacking andpressing alternating layers of piezoceramic material and interdigitalelectrode material. Issartel also discloses boundary discontinuitieswithin the electrode structure which form areas in which electrode edgesdo not make contact with the common electrical collectors of thepiezoactuators and in which the piezoceramic layers are prevented fromtouching one another.

Examples of piezoelectric diaphragms and pumps incorporating the sameare described and shown in PCT Patent Application PCT/US01/28947, filedSep. 14, 2001; U.S. patent application Ser. No. 10/380,547, filed May28, 2003, entitled “Piezoelectric Actuator and Pump Using Same”; U.S.patent application Ser. No. 10/388,589, filed Mar. 17, 2003, entitled“Piezoelectric Actuator and Pump Using Same”, and simultaneously filedU.S. Provisional Patent Application______ (attorney docket: 4209-72),entitled “PIEZOELECTRIC DIAPHRAGM ASSEMBLY WITH CONDUCTORS ON FLEXIBLEFILM”, all of which are incorporated herein by reference.

One challenge in piezoelectric diaphragm technology is to obtain notonly responsiveness to an applied electrical signal, but also asufficient force as exerted through the piezoelectric diaphragm foracting upon a medium such as a fluid, for example. What is needed,therefore, and an object of the technology disclosed herein, is apiezoelectric diaphragm assembly which provides enhanced force.

BRIEF SUMMARY

A diaphragm assembly comprises at least two piezoelectric diaphragmmembers arranged in a stacking direction. An interface layer is situatedbetween adjacent piezoelectric diaphragm members.

In one example embodiment the interface layer in the stacking directionis displaceable but incompressible. The interface layer permits lateralmovement of the adjacent piezoelectric diaphragm members relative to theinterface layer in a direction perpendicular to the stacking direction.The incompressible interface layer can comprise, for example, anincompressible liquid or a semi-liquid. A gasket can be used to seal theincompressible substance in the interface layer if necessary. Due to theincompressible nature of each interface layer, the force applied by thedisplacement of a piezoelectric diaphragm member on a first side of aninterface layer is essentially totally transmitted by the interfacelayer to another piezoelectric diaphragm member on a second side of theinterface layer. As a result, when activated the stacked piezoelectricdiaphragm members yield roughly the sum total of the forces of theindividual piezoelectric diaphragm members bi-directionally and withminimum loss.

In another embodiment the interface layer can be a plastic film, such asa plastic film disk, for example.

The diaphragm assembly can be advantageously employed in manyapplications and devices, such as pumps, compressors, valve actuators,and the like

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a vertical cross section view of an example embodiment of apiezoelectric diaphragm assembly.

FIG. 2 is a vertical cross section view of an example embodiment of apump which incorporates the piezoelectric diaphragm assembly of FIG. 1.

FIG. 3 is a top view of the pump of FIG. 2.

FIG. 4 is a vertical cross section view of an another example embodimentof a pump.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.In other instances, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionof the present invention with unnecessary detail. Moreover, individualfunction blocks are shown in some of the figures.

FIG. 1 shows a cross section of diaphragm assembly 20 capable ofapplying high force bidirectionally. The diaphragm assembly 20 comprisesat least two stacked piezoelectric diaphragm members 22 arranged in astacking direction. The stacking direction, depicted by arrow 23, isessentially parallel to the thickness of each piezoelectric diaphragmmember 22. If the piezoelectric diaphragm members 22 were considered aslying in planes, then the stacking direction 23 would be essentiallyperpendicular to the plane of each piezoelectric diaphragm member 22. Insome embodiments, however, the piezoelectric diaphragm members 22 may beslightly domed due either to formation techniques or structuralrepercussions thereof. In any event, the stacking direction 23 isunderstood to be along the smallest dimension of the piezoelectricdiaphragm members 22.

The particular example, non-limiting embodiment of diaphragm assembly 20illustrated in FIG. 1 happens to comprise three piezoelectric diaphragmmembers 22. A lesser (two) or greater number of piezoelectric diaphragmmembers 22 may be provided in other embodiments. However, as the stackgrows to a greater number of piezoelectric diaphragm members 22, themass of the stack will increase and its mechanical properties may change(stiffness, springiness, dampening from the interface, etc.). Thesefactors may affect speed and displacement at which the stack can bedriven.

A degree of curvature of the piezoelectric diaphragm members 22(relative to stacking direction 23) changes in accordance with appliedvoltage. For example, in the absence of an electrical signal or voltage,the piezoelectric diaphragm members 22 may have a relatively flat orslightly curved configuration as shown in FIG. 1. On the other hand,when a voltage is applied, the degree of curvature of the piezoelectricdiaphragm members 22 increases, so that the centers of the piezoelectricdiaphragm members 22 displace or flex more prominently in the stackingdirection 23.

FIG. 1 further shows that an interface layer 24 is situated between eachadjacent piezoelectric diaphragm members 22. In the embodiment of FIG.1, each interface layer 24 is, in the stacking direction 23,displaceable but incompressible. That is, each interface layer 24 can,in response to flexure or displacement of its adjacent piezoelectricdiaphragm members 22, also flex or displace in the stacking direction23. Yet due to the incompressible nature of each interface layer 24, theforce applied by the displacement of a piezoelectric diaphragm member 22on a first side of an interface layer 24 is essentially totallytransmitted by the interface layer 24 to another piezoelectric diaphragmmember 22 on a second side of the interface layer 24.

Advantageously, while each interface layer 24 is incompressible, theinterface layer 24 also permits lateral movement of the adjacentpiezoelectric diaphragm members 22 relative to the interface layer. Suchlateral movement is in a direction perpendicular to the stackingdirection 23, e.g., along the surfaces of piezoelectric diaphragmmembers 22 which contact the interface layer 24. In other words, theinterface layer 24 is not adhered or bonded to its adjacentpiezoelectric diaphragm members 22, but rather the adjacentpiezoelectric diaphragm members 22 can slip laterally with respect tothe interface layer 24. By allowing such slippage, the interface layer24 does not dampen or impede the displacement of the piezoelectricdiaphragm members 22 when the piezoelectric diaphragm members 22 areactivated by application of a voltage, for example.

Each interface layer 24 is preferably air-tight. The interface layer 24can, in example embodiments, comprise an incompressible substance. Inone example embodiment, the incompressible substance of interface layer24 comprises a liquid. In another example embodiment, the incompressiblesubstance of interface layer 24 comprises a semi-liquid such as curedRoom Temperature Vulcanizing (RTV) silicone adhesive. RTV is a commonliquid adhesive that cures to a rubber-like semi-solid. Any material canserve as interface layer 24 provided that it is incompressible and canflow to some extent. Incompressibility provides bidirectionalitybenefits, and inexpandability. Most liquids, oils, greases, etc., canserve as the interface layer 24, although materials with a low vaporpressure should be avoided as they may cause cavitation in the layerwhen a negative pressure occurs (as in the suction stroke of a pump, forexample). Materials that can be laminated can also serve as theinterface layer 24 and can be laminated into the stack rather than gluedor assembled.

When interface layer 24 comprises a liquid or some semi-liquids, agasket 26 may be required at edges of peripheries of the diaphragmassembly 20 to seal the liquid or semi-liquid in the respectiveinterface layer. FIG. 1 shows an illustrative embodiment where gaskets26 are required. Many flexible adhesives/sealants such as silicones(e.g., RTV), urethanes, epoxies, etc., can serve as the interface layer24, and in so doing can eliminate the need for gaskets 26 and also allowfor realizing stacks as standalone units or actuators (without the needfor something like a pump housing to hold together a stack comprisingthe piezoelectric diaphragm members, the interface layers, and gaskets).Thus, gaskets may not be required for some incompressible substances(e.g., RTV sealant), and therefore can be omitted.

The thickness of the interface layer 24 can be a function of viscosityand mass of the interface material. For example, a very low viscosity,low-mass liquid and a lightweight oil can afford a much thinnerinterface than a silicone adhesive or laminating material. For adhesivesand laminates that comprise the interface layer 24, such adhesiveinterface layer or lamination interface layer should be dimensionallythick enough and flexible enough to allow for a certain degree ofperpendicular movement (perpendicular to the stacking direction of thepiezoelectric elements). Conceptually such adhesive interface layer orlamination interface layer can be considered as if they were very thickfluids. While the adhesive or sealant or flowable lamination layer mayrestrict the perpendicular movement more than a less viscous medium suchas oil, such layers do have offsetting advantages such as easiermanufacturability.

In one example, non-limiting embodiment, each piezoelectric diaphragmmember 22 comprises a piezoelectric material or core which is laminatedbetween a metal substrate layer and an outer metal layer. In thelamination process, an adhesive bonding is employed to laminate themetal layers to the piezoelectric core. The metal substrate layer can becomprised of stainless steel and the outer metal layer can be comprisedof aluminum. It would be apparent to one skilled in the art that othermaterials could be used for the enclosing layers. The structure andfabrication of such an example piezoelectric diaphragm member isunderstood with reference to, e.g., one or more of PCT PatentApplication PCT/US01/28947, filed Sep. 14, 2001; U.S. patent applicationSer. No. 10/380,547, filed May 28, 2003, entitled “PiezoelectricActuator and Pump Using Same”; U.S. patent application Ser. No.10/388,589, filed Mar. 17, 2003, entitled “Piezoelectric Actuator andPump Using Same”, and simultaneously filed U.S. Provisional PatentApplication______ (attorney docket: 4209-72), entitled “PIEZOELECTRICDIAPHRAGM ASSEMBLY WITH CONDUCTORS ON FLEXIBLE FILM”, all of which areincorporated herein by reference.

The incompressible interface layer 24 mechanically locks adjacentpiezoelectric diaphragm members 22 together longitudinally (e.g., in thestacking direction 23). To yield maximum value, such locking ispreferably bidirectional in the stacking direction 23. However, thepiezoelectric diaphragm members 22 are still free to move against eachother laterally. Such lateral freedom may avoid, for example, anylamination stiffness in an embodiment in which the piezoelectricdiaphragm members 22 are laminated. The air-tight nature of theinterface layer 24 yields bi-directional, longitudinal mechanicalrigidity yet allows for the slight lateral movement (advantageous foravoiding lamination stiffness). As a result, when activated the stackedpiezoelectric diaphragm members 22 yield roughly or approximately thesum total of the forces of the individual piezoelectric diaphragmmembers 22 bi-directionally and with minimum loss, e.g., minimum loss interms of mass, friction, or flowability of the in interface layer.

A diaphragm assembly 20 such as that of FIG. 1 can be advantageouslyemployed in many applications and devices, such as pumps, compressors,valve actuators, and the like.

FIG. 2 shows an illustrative embodiment of an example pump 40 whichemploys the diaphragm assembly 20 of FIG. 1. Stacked piezoelectricdiaphragm members 22 can be used as an actuator in pump 40 (for examplereplacing a single piezoelectric diaphragm). Pump 40 of FIG. 2 comprisespump body 42, which may be essentially cylindrical in shape and have acavity therein. The diaphragm assembly 20 is inserted into the cavity tobear against a ring or gasket 44 which extends around an interiorcircumference of the cavity. As such, the gasket 44 essentially definesa thickness of a pump chamber 46, the pump chamber 46 being defined bothby the pump body 42 and the inserted diaphragm assembly 20. An inletport 50 and an outlet port 52 are provided, e.g., in pump body 42 forallowing fluid to enter and exit from pump chamber 46. On a back side ofdiaphragm assembly 20 (a side of diaphragm assembly 20 which is oppositethe pump chamber 46), the diaphragm assembly 20 is retained in thecavity of pump body 42 by a spacer or gasket 54. A pump lid 56 can beprovided over the cavity for further retention of diaphragm assembly 20therein. A vent or access hole 58 can be provided in pump lid 56.

The diaphragm assembly 20 works in conjunction with electrical signalswhich are applied to the piezoelectric diaphragm members 22 thereof. Forexample, metal layers of the piezoelectric diaphragm members 22 maycomprise electrodes to which the electrical signals are applied. Thepump 40 of FIG. 2 shows a drive circuit 60 which generates the drivesignals which are applied to the piezoelectric diaphragm members 22through (unillustrated) electrical leads.

In an example pump having a diaphragm assembly 20 with two piezoelectricdiaphragm members 22 and an interface layer 24 of trapped siliconegrease, a twelve pound per square inch force was delivered from a pumpthat otherwise (with one piezoelectric diaphragm member) would deliver aforce in the range of seven to eight pounds per square inch. The volumeoutput appeared to remain roughly constant.

FIG. 4 shows another embodiment of a pump 40′ having wherein a plasticfilm such as polyamide film, teflon, polyurethane, for example, servesas the interface layer 24′ each adjacent piezoelectric diaphragm members22. The stack of pump 40′ provides unidirectional advantage and issuitable for applications such as some pumping applications whichbenefit from increased pressure but do not require more suction. Theplastic film can have a disk shape, or any appropriate shape given thedesired geometry and configuration (of, e.g., the pump housing). Otherelements of the pump 40′ of FIG. 4 are essentially the same as those ofFIG. 2.

The shape and size of the stack can vary, as can pump features such aspump housing configuration (size, shape, inlet and outlet orientationand positioning, and the like). The drive circuit is not confined to anyparticular type of circuit. Suitable examples include those described inU.S. patent application Ser. No. 10/816,000 (attorney docket 4209-26),filed Apr. 2, 2004 by Vogeley et al., entitled “Piezoelectric Devicesand Methods and Circuits for Driving Same”, which is incorporated hereinby reference in its entirety, or by documents referenced and/orincorporated by reference therein.

The technology described herein thus advantageously couples multiplepiezoelectric diaphragm members in such a way as to yield mechanicalactuators that deliver roughly the sum total of the forces of theindividual piezoelectric diaphragm members and with minimum loss. Inembodiments in which the interface layer is incompressible, themechanical actuators also have bidirectionally.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Noneof the above description should be read as implying that any particularelement, step, range, or function is essential such that it must beincluded in the claims scope. The scope of patented subject matter isdefined only by the claims. The extent of legal protection is defined bythe words recited in the allowed claims and their equivalents. It is tobe understood that the invention is not to be limited to the disclosedembodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements.

1. A diaphragm assembly comprising: at least two piezoelectric diaphragmmembers arranged in a stacking direction; an interface layer situatedbetween adjacent piezoelectric diaphragm members, the interface layer inthe stacking direction being displaceable but incompressible.
 2. Theapparatus of claim 1, wherein the interface layer comprises anincompressible liquid.
 3. The apparatus of claim 2, wherein a gasketentraps the interface layer between the adjacent piezoelectric diaphragmmembers.
 4. The apparatus of claim 1, wherein the interface layer is asemi-liquid.
 5. The apparatus of claim 4, wherein a gasket entraps theinterface layer between the adjacent piezoelectric diaphragm members. 6.The apparatus of claim 1, wherein each piezoelectric diaphragm membercomprises: a piezoelectric core; a metal substrate laminated on a firstside of the piezoelectric core; and an outer metal laminated on a secondside of the piezoelectric core.
 7. The apparatus of claim 1, wherein theinterface layer permits lateral movement of the adjacent piezoelectricdiaphragm members relative to the interface layer in a directionperpendicular to the stacking direction.
 8. A pump comprising: a pumpbody for at least partially defining a pumping chamber, an inlet port,and an outlet port; a diaphragm assembly situated in the pump body, thediaphragm assembly comprising: at least two piezoelectric diaphragmmembers arranged in a stacking direction; an interface layer situatedbetween adjacent piezoelectric diaphragm members, the interface layer inthe stacking direction being displaceable but incompressible.
 9. Theapparatus of claim 8, wherein the interface layer comprises anincompressible liquid.
 10. The apparatus of claim 9, wherein a gasketentraps the interface layer between the adjacent piezoelectric diaphragmmembers.
 11. The apparatus of claim 8, wherein the interface layercomprises a semi- liquid.
 12. The apparatus of claim 11, wherein agasket entraps the interface layer between the adjacent piezoelectricdiaphragm members.
 13. The apparatus of claim 8, wherein eachpiezoelectric diaphragm member comprises: a piezoelectric core; a metalsubstrate laminated on a first side of the piezoelectric core; and anouter metal laminated on a second side of the piezoelectric core. 14.The apparatus of claim 8, wherein the interface layer permits lateralmovement of the adjacent piezoelectric diaphragm members relative to theinterface layer in a direction perpendicular to the stacking direction.